1. Field of the Invention
The present invention relates to a device for detecting an angular displacement relative to absolute space by utilizing the inertia of a liquid and, for example, to an angular displacement detecting device suitable for use in detecting an image shake which may occur during photography using a camera.
2. Description of the Related Art
A conventional angular displacement detecting device of this type is basically constructed as described below in detail, as disclosed in U.S. patent application Ser. No. 355,330, filed on May 23, 1989, and Japanese Laid-open Patent Application Nos. Hei 2-82165 and Hei 2102414. The construction will be explained with reference to FIGS. 3 to 5.
As shown in these figures, the conventional angular displacement detecting device comprises a base 101 to which individual parts for constituting the device are secured in position, and a tubular casing 102 serving as a sealed liquid container having a chamber in which a floating body 103 and a liquid 104 are sealed. The tubular casing 102 has a groove 102a which is formed in its inner wall so as to securely engage with a floating-body support 114 having a U-like cross section as shown in detail in FIG. 5. The floating body 103 has magnetic characteristics, and is supported for rotation about an axis 103a by the floating-body support 114. Mirrors 109 are respectively secured to one pair of opposed side faces of the central block of the floating body 103, and each of the mirrors 109 is covered by a mask 110 having a slit 110a. Arms 103b extend from the other pair of opposed side faces of the central block, respectively. The floating body 103 is constructed so as to maintain the balance of rotation about the axis 103a and the balance of buoyancy in the liquid 104.
It is to be noted that the tubular casing 102 is, as described above, charged with the liquid 104 in a sealed manner.
A light emitting element (IRED) 105, which is adapted to emit light by energization, is secured to the base 101 via a light-emitting-element carrier 107. A light receiving element (PSD) 106 utilizes a photoelectric conversion device whose output varies with the position where light is received, and is fixed to the base 101 via a light-receiving-element carrier 108. The light emitting element 105 and the light receiving element 106 constitute optical angular displacement detecting means of the type which transmits light by means of either of the mirrors 109 secured to the opposed side faces of the central block of the floating body 103. A light guide portion 107a is formed on the light-emitting-element carrier 107 for guiding light emitted from the light emitting element 105, and a mask 110, is secured to the distal end of the light guide portion 107a. The mask 110, has a slit 110a' identical to the slit 110a of the mask 110. Since the light transmission is effected through the tubular casing 102, the whole or a predetermined portion of the tubular casing 102 is formed of a transparent material.
A pair of yokes 119 and 120 is disposed in such a manner as to produce a magnetic field action for holding the floating body 103 having the magnetic characteristics in a fixed position, i.e., in a position where the floating body 103 takes the shown attitude. Ends 119a and 120a of the respective yokes 119 and 120 are opposed to and spaced apart from each other along the diameter of the tubular casing 102 as shown in FIG. 3. A yoke 121 is interposed between the other end portions of the yokes 119 and 120, and a solenoid coil 122 is fitted onto the yoke 121. The above-described arrangement allows a magnetic circuit to be formed by the yokes 119, 120 and 121 and the floating body 103, and a magnetic force is imparted to the floating body 103 by the magnetic force produced by the solenoid coil 122.
The above-described rotatable supporting of the floating body 103 is accomplished in the following manner. As shown in FIG. 4 in cross-sectional form, a rotary shaft 111 extends through the central block of the floating body 103 in the vertical direction, and a pivot 112 having an outwardly pointed end is press-fitted into each of the top and bottom ends of the rotary shaft 111. Pivot bearings 113 are respectively secured to the upper and lower arms of the U-like shape of the above-described floating body support 114 in such a manner that they are opposed to each other in the inward direction. The floating body 103 is supported by the engagement between the pointed ends of the pivots 112 and the corresponding pivot bearings 113.
A lid 115 is bonded to the tubular casing 102 in a sealed manner by a known art utilizing a silicone adhesive or the like. A packing rubber 116 is sandwiched between a pressure disk 117 and the lid 115, and is fixed by screws or the like.
In the above described arrangement, the floating body 103 is constructed so that the balance of rotation about the axis 103a and the balance of buoyancy in the liquid 104 can be maintained as described previously in order to prevent an angular moment from occurring by the influence of gravitation whatever attitude the floating body 103 may take, and to prevent substantial loads from acting on the pivots or the pivot bearings.
According to the above-described arrangement, even if the tubular casing 102 rotates about the rotational axis 103a, an inner portion of the liquid 104 does not move owing to inertia and, therefore, the floating body 103 which is in a floating state does not rotate. As a consequence, the tubular casing 102 and the floating body 103 rotate about the rotational axis 103a with respect to each other. This is the principle of the device for detecting a relative angular displacement, and the relative angular displacement can be detected by the optical detecting means utilizing the light emitting element 105 and the light receiving element 106.
In practice, a flow is produced in the inner portion of the liquid 104 by the influence of the wall surface of the tubular casing 102, and the flow applies a viscosity force to the floating body 103. The influence of the flow, however, can be minimized by appropriately selecting factors such as the distance between the wall surface and the floating body 103 and the viscosity of the liquid 104.
In the device having the above-described arrangement, detection of an angular displacement is accomplished in the following manner.
Light emitted from the light emitting element 105 passes through the light guide 107a and illuminates the floating body 103, and light reflected by an illuminated one of the mirrors 109 reaches the light receiving element 106. As described above, the mask 110, is secured to the distal end of the light guide 107a, while the mask 110 is secured to each of the mirrors 109 of the floating body 103. Accordingly, the light is approximately collimated by the slit 110a of the mask 110 during light transmission, whereby a sharply focused image (slit image) is formed on the light receiving element 106.
The tubular casing 102, the light emitting element 105 and the light receiving element 106 integrally move since all of them are secured to the base 101. If a relative angular displacement occurs between the tubular casing 102 and the floating body 103, the slit image on the light receiving element 106 will move by an amount corresponding to the relative angular displacement. Accordingly, the light receiving element 106, which utilizes a photoelectric conversion device whose output varies with the position where light is received, produces an output substantially proportional to the positional displacement of the slit image. It is, therefore, possible to detect the angular displacement of the tubular casing 102 by utilizing such an output as information.
In the case of the angular displacement detecting device having the above-described arrangement, since the floating body 103 is not subjected to an external force, the attitude of the floating body 103 cannot be restricted. As a result, it might be considered impossible to ensure that the slit image is positioned within the measurement range of the light receiving element 106. However, if, for example, the above-described solenoid coil 122 is used to exert a weak magnetic field action on the floating body 103, the magnetic field action can be made to act as a spring force which produces a force locating the floating body 103 at the steady position shown in FIG. 3.
The spring force exerted on the floating body 103 by the magnetic field action is theoretically a force which maintains the floating body 103 in a fixed attitude with respect to the tubular casing 102, i.e., a force which acts to move the floating body 103 integrally with the tubular casing 102. If such spring force is excessively strong, the tubular casing 102 and the floating body 103 will move integrally, thus resulting in the problem that a relative angular displacement required for a desired angular displacement is not produced. However, if the magnetic field action is made sufficiently small with respect to the inertia of the liquid 104, it is possible to realize an arrangement capable of responding to an angular displacement of relatively low frequency as well.
The liquid 104 sealed in the tubular casing 102 constitutes an important factor which determines the performance and size of the device. Accordingly, the liquid is required to have physical properties such as high specific gravity, low viscosity, light transmission properties, chemical/physical stability and low vapor pressure as well as stable physical properties which do not greatly vary with temperature change.
The specific gravity is useful in that the present detecting device utilizes inertia and as the moment becomes larger, measurement sensitivity is improved, i.e., it becomes possible to detect an angular displacement of lower frequency. The high specific gravity also makes it possible to achieve a compact arrangement without substantially reducing the measurement sensitivity.
The viscosity of the liquid 104 cooperates with the wall surface of the tubular casing 102 to integrally move the tubular casing 102 and the floating body 103. As a result, as the viscosity of the liquid 104 increases, the measurement sensitivity deteriorates. Accordingly, as the viscosity is made smaller, the measurement sensitivity is improved. If the gap between the wall surface of the tubular casing 102 and the floating body 103 is made small, it is possible to achieve a compact arrangement without substantially reducing the measurement sensitivity.
The light transmission properties are required to implement position detection utilizing light emitting and receiving elements.
The chemical/physical stability is required to prevent the liquid 104 from deteriorating by reaction with the tubular casing 102, the floating body 103 or the like. In addition, the chemical/physical stability is required to stably use the device for a long time without swelling or elution of the tubular casing 102, the floating body 103 or the like. Such stability is also required to prevent the liquid 104 from affecting an organism or an environmental system even if the device is broken into element pieces and the liquid 104 is scattered during disposal.
The low vapor pressure is required to prevent an explosion due to evaporation of the liquid during temperature rise or to prevent the liquid from vaporizing through a container during a long service.
If the physical properties tend to greatly vary with temperature change, the characteristics of the device will be greatly influenced by variations in operating environments, with the result that the practicability of the device will be impaired.
As described above, limitations imposed on the liquid are strict. However, a conventional type of liquid generally has the problem that, if its viscosity is made low, the vapor pressure may become high, a tubular casing or a floating body may be swollen, or phenomena such as decomposition of the liquid may occur due to limited chemical stability. As a result, it has been impossible to stably use the conventional liquid for a long time.